Microsoft did change some of the system fonts in Windows Vista which tend to look cleaner and crisper than those used in Windows XP. This comes at no surprise considering that Windows XP is quite a bit older and that font development has made huge progress in the meantime.
It would probably not be legal to simply download and use those fonts in Windows XP but there is a way to get them on the XP system legally.
The reason why you may want to do that is clear: the font is better which means that text will have a better visibility on the system.
The free Powerpoint Viewer 2007 ships with several Windows Vista system fonts which it installs on the system when you run its installer. What’s great about this is that these fonts remain on the system even if you select to uninstall PowerPoint Viewer 2007 from the operating system again.
In theory, you could install the program, make sure the fonts were installed, and remove it again afterwards if you don’t require it without losing access to the new fonts.
The cleartype fonts Calibri, Cambria, Candara, Consolas, Constantia and Corbel are installed to the fonts directory of the Windows XP installation when you install PowerPoint Viewer 2007 on the operating system.
You can change the font that Windows is using in the Appearance tab of the Display Properties. Just click on the Advanced button in that menu and select the element that you want to change the font for.
You should see an immediate difference if you select one of the new fonts and have cleartype enabled.
Users who use a custom design have to make sure that the new font does not break the design as it may be wider than the previously used font. You may change the size of the font or switch to another of the new fonts instead to see if it displays better in that case.